The present invention relates to a new and improved method of, and apparatus for, surface or terrain and space monitoring by means of pulsed directional beams.
There are already known to the art different types of light barriers, such as for instance disclosed in German Patent Nos. 2,157,815 and 2,129,666 and German Patent Publication No. 2,353,702, which can be employed for monitoring, against unauthorized intrusion, certain surfaces, terrain or spaces or areas. Such systems provide intrusion supervision along a periphery, however only along linear paths. Additionally, they are afflicted with the drawback that the equipment needed for such purpose must be erected at the periphery of the monitored terrain or space or the like. Hence, it is possible by, for instance, intentionally or maliciously tampering with the equipment to impair its effectiveness, or else by carefully observing the functioning of the system to take counter measures for fooling the same. There have also been proposed in the art space monitoring systems wherein, at a space which is to be supervised or monitored, there is produced a radiation field. Sensors are provided which are responsive to field changes, as the same are caused by objects, such as intruders, invading the space or area and, in consequence thereof, trigger an alarm. Significant in this regard are the following prior art references: German Patent Publication No. 2,346,764, German Patent Publication No. 2,508,796 German Patent Publication No. 2,600,362, German Patent No. 2,613,375, German Patent No. 2,617,467, German Patent No. 2,638,337, German Patent No. 2,656,256, German Patent Publication No. 2,702,499 and German Patent Publication No. 2,722,982.
Prior art methods and equipment are capable of satisfactorily accomplishing certain objectives or tasks. However, as a general rule they are afflicted with the drawback that, if they are set to possess adequate sensitivity, apart from tripping the desired alarms, they also can be caused to trigger false alarms by the action of some other effects. Such system operation is, however, unsatisfactory on a continuing basis, since upon frequently triggering false alarms the confidence in the reliability of such method and its equipment oftentimes is so shaken or impaired that, with time, there is a tendency not to take too seriously the triggering of an alarm.